1. Field of the Invention
This invention relates to a ball valve, more particularly to a ball segment valve.
2. Description of the Related Art
In many chemical industrial and manufacturing applications, ball valves are commonly used to regulate fluid flow in pipes. However, when a fluid containing solid particles, such as plant fibers, glass fibers, carbon fibers, etc., passes through a ball valve in a pipe, the solid particles may be trapped between a ball and a sealing assembly of the ball valve to obstruct the closing thereof. Additionally, due to high frictional resistance generated by the solid particles in the fluid, a relatively high mechanical effort to move the ball valve between closed and opened states is required so as to raise consumed power, particularly when the ball valve is actuated by a servo motor.
In view of the aforesaid problem, a ball segment valve, such as that disclosed in U.S. Pat. Nos. 5,820,103, 4,989,833, or WO 2005/040655 A1, has been proposed in which a partial segment of a full ball is provided so as to prevent obstruction of the closing of the valve. However, when the ball segment valve is in a fully closed position, a spindle that rotates the ball segment is subjected to a relatively large pressure of the fluid flow, which may adversely affect maintenance operation of the valve. Specifically, a sealing assembly provided to seal engagement between the spindle and a valve body of the ball segment valve may easily become worn due to a repeated rotation of the spindle relative to the sealing assembly, and has to be replaced regularly. Since the fluid pressure in the pipe may need to be lowered before replacing the sealing assembly, the overall fluid flow may have to be reduced, thereby adversely affecting subsequent operations, such as a reduction in paper pulp supply, in a paper manufacturing process.